Optical objective system with interchangeable varifocal and telescopic lens groups



Jan. 16, 1968 K. H. MACHER 3,363,964

OPTICAL OBJECTIVE SYSTEM WITH INTERCHANGEABLE VARIFOCAL AND TELESCOPIC LENS GROUPS Filed Dec. 23, 1964 2 Sheets-Sheet 1- '7 6120 d22 fro i d27 d28 d50d31 L15 L17 L18 1.19 LID uvuz u: -v-

m Y Inventor;

Karl Heinrich Macher AGENT.

Jan. 16, 1968 K. H. MACHER 3,363,964

OPTICAL OBJECTIVE SYSTEM WITH INTERCHANGEABLE 4 VARIFOCAL AND TELESCOPIC LENS GROUPS Filed Dec 23, 1964 2 Sheets-Sheet P,

INVENTOR.

AGENT United States Patent 3,363,964 OPTICAL OBJECTIVE SYSTEM WITH INTER- CHANGEABLE VARIFOCAL AND TELE- SCOPIC LENS GROUPS Karl Heinrich Macher, Bad Kreuznach, Germany, assignor to Jos. Schneider & Co., Bad Kreuznach, Rhineland, Germany, a corporation of Germany Filed Dec. 23, 1964, Ser. No. 420,650 Claims priority, application Germany, Jan. 9, 1964, Sch 34,429 6 Claims. (Cl. 350-176) The present invention relates to a varifocal optical objective system for photographic or cinematographic cameras of the general type disclosed in my copending applications Ser. No. 291,851 filed July 17, 1963, now Patent No. 3,235,700, and Ser. No. 401,128 filed Oct. 2, 1964.

A system of this type includes a fixed rear lens group or basic objective and an adjustable front lens group or varifocal attachment, the latter consisting of two substantially stationary outer components of positive refractivity bracketing two axially movable inner components of negative refractivity. The term substantially stationary allows for the possibility that an element of either of these positive components, especially a front lens forming part of the first component as seen from the object side of the system, may be limitedly displaceable for focusing purposes.

In the system disclosed in my above-identified copending applications, as well as in a broadly similar system forming the subject matter of commonly assigned application Ser. No. 126,306 filed Feb. 24, 1961 by Giinter Klemt and me, and now abandoned, the first movable component (i.e. the second component as seen from the object side) consists of two air-spaced lens members whereas the two following components of the varifocal group are constituted by individual lens members; in an objective of the type shown in my copending applications referred to, the positive first component of the varifocal group consists of four air-spaced singlets of large diameter including a dispersive front lens followed by three collective lenses.

It is an object of my present invention to provide a high-speed varifocal system of this character so proportioned in its radii of curvature and other optically effective parameters that the diameters of the lenses of the first component can be considerably reduced without objectionable vigetting.

Another object of this invention is to provide a system of this type which is operative over a wide varifocal range, such as 6:1, and with a large relative aperture, such as 1:1.8, yet which is structurally simplified through replacement of the two-member second component of the earlier systems by a single lens member of negative refractivity.

It is also an object of this invention to realize the aforestated advantages along with a high degree of achromatism and correction for spherical aberrations, astigmatism, field curvature and coma.

A further object of this invention is to provide, in an objective system having the qualities set forth above, means for optionally replacing its varifocal front group by a fixed-focus attachment designed to shorten the eflective focal length of the basic objective and to compensate for any aberrations, especially chromatic ones, that would be present in this basic objective upon removal of the varifocal front attachment.

A particular field of application for the present improvement is a cinematographic camera objective designed for 8-mm. motion-picture film with a short focal length of, say, 13 mm. and with a diaphragm positioned at close distance from the image plane just ahead of the last lens of the basic objective, there being preferably also provided a reflex prism ahead of the fixed rear lens group.

3,363,964 Patented Jan. 16, 1968 I have found that, especially in the case of a system of the type just mentioned in which a diaphragm must be positioned close to the rear vertex for structural reasons, the entrance pupil can be moved close enough to the front to permit a desirable reduction of lens diameters if, in conformity with a feature of this invention, the absolute value of the individual focal length of the negatively refracting second component of the varifocal group is greater than one-half the individual focal length of the positive first component of that group and if, concurrently, the absolute value of the individual focal length of the negative third component is less than 0.7 times the individual focal length of the positive fourth component of the group. 7

Another feature of my invention, designed to afford good correction of residual aberrations, resides in such a dimensioning of the negatively refracting movable second and third components of the varifocal group that the absolute ratio of the radii of curvature of the less strongly concave rear surface and the more strongly concave front surface of the third component is less than one-tenth the absolute value of the ratio of the radii of curvature of the slightly convex front surface and the strongly concave rear surface of the second component. For improved achromatism I prefer, pursuant to still another feature of this invention, to design each of these movable components as a doublet with a positively refracting cemented surface, the absolute ratio of the larger radius of curvature of the preferably forwardly concave cemented surface of the second component and of the smaller radius of curvature of the preferably forwardly convex cemented surface of the third component being greater than 10.

Yet another feature of my invention involves the provision of means for replacing the aforedescribed fourcomponent varifocal group by a fixed-focus attachment consisting of two air-spaced lens members of opposite refractivity adapted to compensate for residual chromatic aberrations of the basic objective. These lens members may be singlets, in which case they should be made of glass with a refractivity index greater than 1.7 and an Abb number less than 40; they could also be designed as doublets, however, in which event less expensive glasses with lower refractive indices may be used. In a system of the latter type I have found it to be advantageous, for optical correction, to make the cemented surfaces of the two doublets positively refracting and of opposite curvature, the absolute ratio of the radii of curvature of these two surfaces being preferably close to unity and in any case not greater than 3.

The invention will be described hereafter with greater detail, reference being made to the accompanying drawing in which:

FIG. 1 is a lens diagram illustrating a complete varifocal objective system embcdying the invention;

FIG. 2 is a diagram showing the varifocal front group of the system of FIG. 1 replaced by a fixed-focus twomember front attachment;

FIG. 3 is a view similar to FIG. 2, showing a modified two-member attachment; and

FIG. 4 is an elevational view (parts broken away) of a camera having a varifocal objective with interchangeable front attachments in accordance with FIGS. 1 and 2.

The system shown in FIG. 1 comprises a varifocal group consisting of four components I, H, HI and 1V removably positioned in front of a fixed basic objective V. Component I consists of a biconcave front lens L1 with radii r1, r2 and thickness d1, a first biconvex lens L12 with radii r3, r4 and thickness d3, a second biconvex lens L3 with radii r5, r6 and thickness d5, and a meniscusshaped further positive lens L4 with radii r7, r8 and thickness d7, these four lenses being separated from one am component I from the axially movable negative component II which is in the form of a doublet composed of a 4 thickness d27) and L17 (radii r30, r31, thickness 1128), the associated positively refracting member being also a doublet composed of a lens L18 (radii r32, r33, thickness d30) and a lens L19 (radii r33, r34, thickness d31). The air space separating the two members of group VII positive lens L5 (radii r9, r10, thickness d9) and a negahas been designated d29. tive lens L6 (radii r10, r11, thickness d); another varia- In both FIG. 2 and FIG. 3 the air space d16 accomble air space dll intervenes between this component and modating the prism P has the same magnitude as in the the second movable negative component III, also in the system of FIG. 1. form of a doublet, which consists of a negative lens L7 10 In the following Table A, I have listed representative (radii r12, r13, thickness d12) and a positive lens L8 numerical values for the radii rl-r24, the thickness and (radii r13, r14, thickness d13). Yet another variable air air spaces d1-d23, the refractive indices n and the Abb space d14 separates component III from the fixed posinumbers 1! of a system as shown in FIG. 1, constituting tive component IV constituted by a single lens L9 (radii an objective with a relative aperture of 1:1.8 and a varir15, r16, thickness 4115). A relatively large air space d16, 5 focal range of to 200 linear units; each linear unit may adapted to receive a reflex prism P, is formed between represent a length of 0.2 mm. so that the system would component IV and the concavoconvex first positive lens have minimum and maximum focal lengths of 7 and L10 (radii r17, r18, thickness 1117) of rear lens group mm. respectively. The back-focal length s measures V, this lens being separated by an air space d18 from anunits or 9 mm.

TABLE A Compo- Lens Radil Thicknesses and m r nent Air Spaces d2 =8.50 Airspace r3 =+627.10 L2 d3 =21.50 1. 62041 60.29

r4 =-527.10 I d4 =0.50 Air Space d6 =0.50 Air Space r7 =+171.55 L4 a7 =30.00 1. 62041 60.29

d8 =5.10145.60 Var. Air Space r9 =+944.50 L5 59 =12.50 1.80518 25.46 II r10=-1,832.5o

L6 dlO =5.00 1.51821 65.18

1111 =95.30-28.50 Var. Air Space 112=-137.95 L7 d12 =5.00 1.71300 53.89 111 rl3=+57.00

an =77.10-3.40 Var.Alr Space I r15=+349.40 IV L9 d15 =5.00 1.55830 57.29

dlfi =35.00 Air Space (Prism) r17=+59.95 L10 517 =9.00 1.59181 58.25

1118 =0.50 Airspace r19=+37.25 L11 d19 =13.00 1.71300 53.89

r20=+86.90 v.-- d20 -2.00 Air Space r21=-475.00 L12 d21 =5.00 1.80518 25.40

. 1122 =11.55 Air Space r23=+l21.00 L13 92a =8.35 1.02280 56.88

dnui=404.85

other concavoconvex positive lens L11 (radii r19, r20, The system representative of the foregoing Table A has thickness d19); a biconcave lens L12 (radii r21, r22, individual focal lengths h-f for the various components thickness d21), constituting the sole negative member of as listed below: group V, is separated from lens L11 by an air space d20 TABLE B and from the final lens L13 (radii d23, d24, thickness f =+274,60 d23) by an air space 1122 containing a diaphragm D. At f =-150 28 s' I have indicated the back-focal length of the system as f 112 55 measured between the rear vertex of lens L13 and the f =+176 65 image plane IP. f =+77 50 In FIG. 2 I have shown the varifocal attachment I-IV replaced by a lens group VI consisting of a single bicon- 1 It i B that the system of cave lens L14 (radii r25, r26, thickness d24) separated sans est e re auons by an air space d25 from a single biconvex lens L15 (radii r27, r28, thickness d26).

According to FIG. 3, the group VI has been replaced by the group VII whose negatively refracting first member I is a doublet composed of two lenses L16 (radii r29, r30,

and

and that Upon adjustment of the system for different overall focal lengths f, the variable air spaces d8, dll and d14 assume the values given in the following Table C:

TABLE 0 f 35 mm. 50 mm. 100 mm. 150 mm. 200 mm.

as 5.10 47.40 111. 40 135.40 146.60 1111 95. so 57. 0o. 15. 30 16.15 28.50 1114 77. 10 73.10 50.80 25.95 a. 40

The parameters of group VI (FIG. 2) are listed in the following Table D for a system VI-V whose overall focal length has a magnitude of 66.5 units or about 13' TABLE D Compo- Thicknesses nent Lens Radii and Air m r Spaces VI d25=20.85 Air Space Corresponding parameters for the group VII of FIG. 3 are listed in the following Table E, again for a system The relative aperture and the back-focal length 5" of the system of FIGS. 2 and 3 have the same values as in the varifocal objective system of FIG. 1 (Table A).

It will be seen that the radii r30 and r33 of the oppositely curved and positiyely refracting cemented surfaces of doublets L16 L17 and LlS-L19 satisfy the relationship In FIG. 4 I have shown a motion-picture camera 10 with lens mount 11, a viewfinder 12. and a turret 13 rotatable on a stud 14 by means of a handle 15, this turret supporting two further lens mounts 16 and 17. Lens mount 11 accommodates the prism P and the elements (not shown in FIG. 4) of the fixed lens group V shown in FIGS. 1-3; lens mount 16 supports the varifocal attachment I-IV of FIG. 1 (partially illustrated in FIG.

4) whose movable components H, 111 can be shifted by a handle 18 to vary the overall focal length, whereas lens mount 17 holds the lenses of group VI of FIG. 2. It will be understood that mount 17 could alternatively accommodate the lenses of group VIII (FIG. 3). Thus, rotation of the turret 13 by handle 15 will selectively align the basic objective with either the attachment I-IV. or one of the attachments VI, VII.

I claim: 1

1. An optical objective system with an overall focal length variable between a minimum overall focal length and a maximum overall focal length through three intermediate overall focal lengths, said system comprising:

a fixed-focus rear lens group consisting of a first positive singlet, a second positive singlet, a negative singlet following one another in the order named; and

a varifocal forward lens group consisting of:

a substantially fixed positive first element consisting of three air-spaced positive lenses and a dispersive front lens preceding said three airspaced positive front lenses,

an axially movable second component consisting of a first dispersive lens member in the form of a doublet with a positively refracting cemented surface,

an axially movable negative third component consisting of a second dispersive lens member in the form of a doublet with a positively refracting cemented surface, and

a substantially fixed positive fourth component. consisting of a single collective lens member;

said second and third components being movable relatively to each other and to said first and fourth components through five positions corresponding respectively to said minimum overall focal length, said three intermediate overall focal lengths and said maximum overall focal length, the numerical values of the radii of curvature (r1 to r24) of said dispersive front lens L1, said three air-spaced positive lenses (L2, L3, L4), said first dispersive lens member (L5, L6), said second dispersive lens member (L7, L8), said fourth component L9, said first positive singlet L10, said second positive singlet L11, said negative singlet L12 and said third positive singlet L13, of the axial thicknesses and air spaces (d1 to d23) thereof, based upon numerical values of 35 and 200, respectively, for said minimum and maximum overall focal lengths of the system, the refractive indices n of the lenses (L1 to L13) and their Abb numbers v being substantially as given in the following table with the values of (d8, d11 and d14) being given for said min mum overall focal length:

Com- Thicknesses pon ent Lens Radil and 11.1 v

Spaces d2 =8. 50 Air S )ece r3 +627. 10 L2 113 =27. 50 1. 62041 60. 29

f4 627. 10 1 I d4 =0. 60 Air Space d6 =0. 50 Air Space r7 =+171. 55 L4 (17 =30. 00 1. 62041 60. 29

d8 =5. 10 Air Space 19 +944 50 L5 (19 =12. 50 1. 80518 25. 46 II r10= 1,832.50

d11=95. 30 Air Space r12= 137. L7 d12= 5. 00 1. 71300 53. 89 III r13= +57. 00

Com- Thicknesses ponent Lens Radii and Air m w Spaces L114: 77. Air Space r= +349. IV L9 d15= 5. 00 1. 65830 57. 29'

d16=35.00 Space r17= +59. 96 L10 4117 =9. 00 1. 59181 58. 25

d18=0. Air S ace r19= +37. 25 L11 1119: 13. 00 1. 71300 53.89

r20= +86. 90 V 1120: 2. 00 Air Space d22=11. Air Space r23= +121. 00 L13 d23=8. 35 1. 62280 56. 88

2. A system as defined in claim 1 wherein said spacings (d8, dll and d14) have values in positions of said second and third components corresponding respectively to intermediate overall focal lengths of numerical values of 50, 100 and 150 and to said maximum overall focal length of 200 as given in the following table:

f 50 mm. 100 mm. 150 mm. 200 mm.

4. A system as defined in claim 3 wherein said front 45 lens group consists of a negative member and a positive member air-spaced from said negative member and disposed rearwardly thereof.

5. A system as defined in claim 4 wherein the numerical values of the radii of curvature (r25 to r28) and the thicknesses and air spaces ((124 to d26) of said negative member L14 and said positive member L15, their refractive indices n and their Abb numbers 1 are substantially as given in the following table:

Lens Radii Thicknesses M v and Air Spaces r25 392. 80 L14 d24=7. 50 1. 75602 31. 74

d25=20. Air Space r27= +196. 05 L15 d26= 12. 50 1. 78470 26.10

6. A system as defined in claim 4 wherein said negative member consists of two cemented lenses (L16, L17) and said positive member consists of two cemented lenses (L18, L19), the numerical values of the radii of curvature (129 to r34) and the thicknesses and air spaces (d27 to d31) of said cemented lenses, their refractive indices n and their Abb numbers 11 being substantially as given in the following table:

DAVID H. RUBIN, Primary Examiner.

JOHN K. CORBIN, Examiner.

R. I. STERN, Assistant Examiner. 

1. AN OPTICAL OBJECTIVE SYSTEM WITH AN OVERALL FOCAL LENGTH VARIABLE BETWEEN A MINIMUM OVERALL FOCAL LENGTH AND MAXIMUM OVERALL FOCAL LENGTH THROUGH THREE INTERMEDIATE OVERALL FOCAL LENGTHS, SAID SYSTEM COMPRISING: A FIXED-FOCUS REAR LENS GROUP CONSISTING OF A FIRST POSITIVE SINGLET, A SECOND POSITIVE SINGLET, A NEGATIVE SINGLET FOLLOWING ONE ANOTHER IN THE ORDER NAMED; AND A VARIFOCAL FORWARD LENS GROUP CONSISTING OF: A SUBSTANTIALLY FIXED POSITIVE FIRST ELEMENT CONSISTING OF THREE AIR-SPACED POSITIVE LENSES AND A DISPERSICE FRONT LENS PRECEDING SAID THREE AIRSPACED POSITIVE FRONT LENSES, AN AXIALLY MOVABLE SECOND COMPONENT CONSISTING OF A FIRST DISPERSIVE LENS MEMBER IN THE FORM OF A DOUBLET WITH A POSITIVELY REFRACTING CEMENTED SURFACE, AN AXIALLY MOVABLE NEGATIVE THIRD COMPONENT CONSISTING OF A SECOND DISPERSIVE LENS MEMBER IN THE FORM OF A DOUBLET WITH A POSITIVELY REFRACTING CEMENTED SURFACE, AND A SUBSTANTIALLY FIXED POSITIVE FOURTH COMPONENT CONSISTING OF A SINGLE COLLECTIVE LENS MEMBER; SAID SECOND AND THIRD COMPONENTS BEING MOVABLE RELATIVELY TO EACH OTHER AND TO SAID FIRST AND FOURTH COMPONENTS THROUGH FIVE POSITIONS CORRESPONDING RESPECTIVELY TO SAID MINIMUM OVERALL FOCAL LENGTH, SAID THREE INTERMEDIATE OVERALL FOCAL LENGTHS AND MAXIMUM OVERALL FOCAL LENGTH, THE NUMERICAL VALUES OF THE RADII OF CURVATURE (R1 TO R24) OF SAID DISPERSIVE FRONT LENS L1, SAID THREE AIR-SPACED POSITIVE LENSES (L2, L3, L4,), SAID FIRST DISPERSIVE LENS MEMBER (L5, L6,), SAID SECOND DISPERSIVE LENS MEMBER (L7, L8), SAID FOURTH COMPONENT L9, SAID FIRST POSITIVE SINGLET L10, SAID SECOND POSITIVE SINGLET, L11, SAID NEGATIVE SINGLET L12 AND SAID THIRD POSITIVE SINGLET L13, OF THE AXIAL THICKNESSES AND AIR SPACES (D1 TO D23) THEREOF, BASED UPON NUMERICAL VALUES OF 35 AND 200, RESPECTIVELY, FOR SAID MINIMUM AND MAXIMUM OVERALL FOCAL LENGTHS OF THE SYSTEM, THE REFRACTIVE INDICES ND OF THE LENSES (L1 TO L13) AND THEIR ABBE NUMBERS V BEING SUBSTANTIALLY AS GIVEN IN THE FOLLOWING TABLE WITH THE VALUES LF (D8, D11 AND D14) BEING GIVEN FOR SAID MINIMUM OVERALL FOCAL LENGTH: 